1. Field of the Invention
The present invention relates to a detection method of a display device. More particularly, the present invention relates to detection method of a display device including pixel devices constructed by organic light emitting diode.
2. Description of Related Art
With the rapid advancement of multimedia technology, semiconductor component and display device technology have progressively developed. In the conventional flat display device, since thin film transistor active matrix organic light emitting diode (TFT-AMOLED) display has the advantages of free of view-angle dependence, low cost, high response speed (about hundreds of times compared to liquid crystal display device), low power consumption, portability, large operating temperature range, light weight and sizable for suiting thinner and miniature requirements, the TFT-AMOLED display can be readily applied in multimedia display device. Therefore, the TFT-AMOLED display has great potential and may be developed as the next generation flat panel display.
Conventionally, the process for manufacturing TFT-AMOLED display may be classified into two methods, one is low temperature polysilicon (LTPS TFT) technology, and the other is amorphous silicon TFT (a—Si TFT) technology. Table I listed below illustrates the comparison of the two technologies.
TABLE 1LTPS TFTa-Si TFTMobility50 to 2000.5 to 1TFT TypePMOS and NMOSNMOSTFT UniformityworsebetterNumber of Process9 to 10 masking4 to 5 maskingprocessesprocessescost (array only)highlowcost (panel module)low (built-in driver)high (external driver)Equipment InvestmenthighlowYieldlowhighOverall Costcheaper in small sizecheaper in large sizepanelpanelOutput Current StabilityhighlowOLED Degradationnot sensitivesensitive
As shown in table 1, it is noted that the uniformity of the TFT-AMOLED display manufactured by the LTPS TFT technology is not good, and the cost of LTPS TFT technology is high due to comparatively larger number of masking processes. Therefore, conventionally, the LTPS TFT technology is mainly adopted for small size panel, however, the a—Si TFT technology is provided for large size panel usually.
Although the cost for manufacturing the TFT-AMOLED display may be reduced by using a—Si TFT technology, however, the a—Si TFT has a variety of disadvantages. FIG. 1A is a plot illustrating the drain current (Id) and gate voltage (Vg) versus time of conventional a—Si TFT. As shown in FIG. 1A, the drain current Id of a—Si TFT will shift after working a period of time.
FIG. 1B and FIG. 1C are plots illustrating the comparison of properties between a—Si TFT and LTPS TFT. As shown in FIG. 1B, the horizontal axis represents time, and the vertical axis represents an output current value, wherein the LTPS TFT has a much better output current stability, however, the output current of the a—Si TFT decays after working for a period of time. In FIG. 1C, the horizontal axis represents time, and the vertical axis represents brightness. It is noted that, the brightness of the AMOLED display manufactured by LTPS TFT technology is very stable even after working for a period of time since the output current stability of LTPS TFT technology is very good. However, the brightness AMOLED display manufactured by a—Si TFT technology decays after working for a period of time since the output current stability of a—Si TFT technology is poor. Therefore, how to compensate a—Si TFT technology to enhance the stability of the AMOLED display using a—Si TFT technology is very important.